C. B. METZ 47 



but that the sugars and amino acids are interhnked. In any event 

 such interhnking is probably not a simple alternation of amino 

 acids and sugars since fertilizin contains peptide linkages as in- 

 dicated by a positive biuret reaction and inactivation by proteo- 

 lytic enzymes (Tyler and Fox, 1940). 



As might be expected from their- high sulfate content fertilizins 

 are strongly acidic proteins. Even near pH 2 they migrate rapidly 

 to the anode during electrophoresis (Runnstrom, Tiselius, and 

 Vasseur, 1942; Tyler, 1949; Tyler, Burbank, and Tyler, 1954b). 



Values for the molecular weight of fertilizin have been cal- 

 culated from ultracentrifugation data. Earlier values [e.g., 82,000 

 for S, purpuratiis fertilizin (Tyler, 1949)] were based on the 

 assumption of a spherical molecule. However, the fertilizin 

 molecule is clearly not spherical for the substance forms gels, 

 precipitates as fibrils (Monroy, 1955), exhibits flow birefringence, 

 and gives sedimentation values that vary with concentration. 

 Accordingly, revised estimates of the molecular weight and axial 

 ratios have been made from more recent sedimentation and dif- 

 fusion data. These give for Arbacia pimctulata fertilizin a molec- 

 ular weight of 300,000 and an axial ratio of 28:1 (Tyler, Burbank, 

 and Tyler, 1954a; Tyler, 1956 ) . When corrected for water of hy- 

 dration, this axial ratio becomes 20:1 (Tyler, 1956). 



Apparently no detailed study of the chemistry of univalent sea 

 urchin fertilizin has yet been made. Univalent fertilizin, like the 

 multivalent agent, is nondialyzable (Tyler, 1941) and gives the 

 mucin-clot reaction, indicating that the univalent fragments are 

 relatively large stable subunits of fertilizin (Krauss, 1949). Pro- 

 duction of the univalent agent by proteolytic enzymes indicates 

 that peptide bonds may form one type of linkage between such 

 units. 



Clear understanding of the chemistry of the "reactive groups" 

 of fertilizin has yet to be obtained. Studies of Arbacia punctulata 

 fertilizin with a series of "protein group reagents" ( Metz, 1954c; 

 Runnstrom, 1935 ) showed that free S — S, SH, phenolic and amino 

 groups are not essential constituents of the receptor groups of 

 fertilizin. Strong oxidizing agents (H2O2) destroy the sperm ag- 

 glutinating action by conversion to the univalent form. They fail 



